The zero-day flaw is apparently quite difficult to exploit, and only skilled engineers with enough time to exploit the flaw might be able to take advantage of it. The flaw could potentially grant a hacker remote access control over the target machine.You can read the detailed article posted by The Guardian here.
Microsoft has published the warning, and is urging people to download and install a tool called "Enhanced Mitigation Security Toolkit", while they work on a patch for the found flaw. The installation is straight forward, and has a couple of default configuration settings that will make it quite easy to setup and mitigate potential exploits in your system. The tool comes with a guide document which also explains how the exploit works and what the tool does to prevent it. You can download the tool here. Check the tool screenshots below.